Studies of voluntary movement focused on the role of the cerebellum. One issue was the contribution of the cerebellum to coordination. The results seem to indicate that the cerebellum is critical to the portion of the motor execution process involving compensation for limb dynamic changes during high-speed movements. A second issue is the role of the cerebellum in motor learning. Tasks are being developed to assess motor skill learning. A study was done of the role of the silent period in the antagonist muscle prior to a ballistic movement. Using O-15 labelled water as a marker for cerebral blood flow in positron emission tomography ( PET) studies, we have been working on methods for improved anatomical correlation of regions of metabolic change by superimposing the PET image onto an MRI image. Studies include analysis of the role of the cerebellum in motor learning and the supplementary motor area in self-paced movement. In evoked potential studies, we have been assessing changes in topography of sensory potentials with lesions of the central and peripheral nervous system looking for evidence of plasticity. Studies of the N30 component of the median nerve sensory evoked potential was found to be enhanced in patients with dystonia. In studies of movement related potentials, we have studied patients with Parkinson's disease, cerebellar degenerations and dystonia. Abnormalities in the first two groups suggest disturbances in the cortical control of movement in these patients. Studies in the Biomechanics Laboratory of the Department of Rehabilitation Medicine have focused on the control of balance and gait. In a study of balance in aging, we found that older normal subjects maintain a more rigid posture, utilizing large and inconsistent adjustments to maintain stability. This may relate to the instability of stance in the elderly.